Without limiting the scope of the invention, its background is described in connection with a fully implantable device for cardiac compression. During a cardiac cycle, the heart expels oxygenated blood into the aorta as its left ventricle contracts (i.e., during systole) and, thereafter, receives a backflow of arterial blood into the coronary arteries as its left ventricle relaxes (i.e., during diastole). The systolic pumping of blood into the aorta requires the myocardium to overcome the static pressure of blood that is already in the aorta. A healthy heart is typically able to perform both of these functions effectively. However, a weakened or failing heart may be unable to perform the work required to fully overcome the static pressure of blood already in the aorta, thereby resulting in less ejection of oxygenated blood into the aorta during systole and less backflow of oxygenated blood into the coronary arteries during diastole. There are various methods of providing assistance to the failing myocardium.
Direct cardiac compression devices are generally known as disclosed first by Anstadt and later by Criscione and are effective in providing assistance to the failing myocardium by generally adding external pressure to help the heart muscle to contract. Generally these devices include a jacket positioned around the heart and containing inflatable bladders that are inflated to coincide with contraction of the myocardium during systole. Operation of such device is supported by a driver configured to inject fluid through a drive line to cause the bladders to expand and withdrawal of fluid during diastole causes the bladders to collapse in preparation for the next systole of the heart. The presence of the drive line exiting the subject is generally undesirable as it may be a source of infection, especially for patients requiring long-term or permanent support. One difficulty associated with injecting and removing a certain volume of drive fluid is the changing volume of the drive system. This changing volume of the drive system makes an implantable driver with changing internal volume problematic, due to the positioning of the device inside the subject so as to not periodically compress surrounding tissues.
U.S. Pat. No. 4,813,952 entitled, “Cardiac Assist Device,” discloses a muscle-powered pump to assist the natural heart, the entire contents of which are incorporated herein by reference. The device comprises an oblate, spheroidal-shaped pumping chamber surrounded by innervated muscular tissue. The device may be coupled to the ventricle and descending aorta with valves and be stimulated in synchrony with the natural depolarization of the heart or the device may be inserted into the descending aorta and used as a counterpulsation device. In this application, the innervated muscle is stimulated after a brief delay from the natural cardiac depolarization.
U.S. Patent Publication No. 2007/0129796 entitled, “Actuator for a heart assist device,” discloses an actuator for a heart assist device having an inflatable balloon and a shroud or wrap.